1. Field of the Invention
The present invention relates to an emergency operation for an elevator system, and more particularly to an improved apparatus and method for controlling an emergency operation of an elevator system during a power failure in the elevator system, which is capable of easily determining respective driving directions of elevator cars.
2. Description of the Background Art
In a general elevator system, there may be provided an auxiliary system to guide an elevator car to the nearest floor for a safe rescue of passengers aboard the car in case of an electrical power failure during its operation. Such an auxiliary system is referred to as ALP (Automatic Landing for Power failure).
When there is a power failure in the system, the ALP powered by a battery serves to convert a direct current voltage of the battery into an alternating current voltage, which is in turn supplied to the elevator system, thereby enabling the passengers aboard the elevator car to be safely rescued.
As shown in FIG. 1 illustrating a conventional emergency control apparatus of an elevator system, the control apparatus includes a source 1 of main (utility) power; a switching node 2 that is connected only during the normal supplying of power from the power source 1; a converter 3 converting the alternating current voltage that has passed through the switching node 2 into a direct current voltage, and supplying the direct current voltage to an inverter 7; the inverter 7 converting the received direct current voltage into alternating current voltages with three phases and three phase frequencies; an induction motor 9 driven by the alternating current voltages with three phases and three phase frequencies; a pulley 12 engaged to a shaft driven by the induction motor 9; a brake 11 for controlling a car operation; a balance weight 17 which weighs an amount obtained by adding the car weight and one-half of a reference load on the car; a load detector 16 detecting the load in a cage 15; a speed detector 10 for detecting an angular velocity of the induction motor 9; a current detector 8 detecting the current that flows through a first coil of the induction motor 9; a control circuit 14 receiving respective output signals from the current detector 8, the speed detector 10 and the load detector 16, transmitting a control signal to a semiconductor device 6 that allows the current to flow through a resistor resistance 5 for thereby consuming a regenerative power, and outputting a voltage command to the inverter 7 that controls the induction motor 9; a transformer 13 providing a supply voltage to the control circuit 14; and an emergency power supply unit 19 providing the supply voltage from the battery 20 to the elevator system through a switching node 18.
FIG. 2 is a block diagram detailing the conventional emergency control apparatus of FIG. 1 during a power failure. As shown therein, the control apparatus includes; the control circuit 14; the load detector 16 supplying a load weight signal W.sub.L to the control circuit 14; the current detector 8 supplying a current signal I to the control circuit 14; the speed detector 10 supplying phase signals .phi..sub.A, .phi..sub.B to the control circuit 14; the inverter 7 receiving a voltage command signal V* outputted from the control circuit 14; and the induction motor 9 being controlled by an output signal from the inverter 7.
The control circuit 14 includes a load detection unit 27 receiving the load weight signal W.sub.L of the cage 15, which is detected by the load detector 16; a speed detection unit 28 for receiving the phase signals .phi..sub.A, .phi..sub.B from the speed detector 10 and calculating therefrom an angular velocity signal .omega..sub.r of the induction motor 9; a driving direction setting unit 21 receiving an output signal from the load detection unit 27 and the angular velocity .omega..sub.r from the speed detection unit 28, and determining a car driving direction; a speed command generator 22 receiving an output signal from the driving direction setting unit 21 and outputting a speed command .omega..sub.r *; a first subtractor 23 outputting a difference signal between the speed command .omega..sub.r * and the angular velocity .omega..sub.r ; a speed controller 24 amplifying the difference signal outputted from the first subtractor 23 and outputting a current command I*; a second subtractor 25 outputting a difference between the current command I* and the current I; and a current controller 26 amplifying the difference outputted from the second subtractor 25 and outputting a voltage command V*.
FIG. 3 is a schematic view illustrating the load detector 16. As shown therein, the load detector 16 is accompanied by a pair of vibration-absorbing rubbers 30 provided between the bottom of the cage 15 and an elevator car casing 29.
FIG. 4A is a graph illustrating the relation between node state and load weight, and FIG. 4B is a graph illustrating the relation between voltage and load weight.
The operation during a power failure of the above-described conventional emergency control apparatus of FIG. 1 for an elevator system will now be explained.
When the supply voltage from the power source 1 is normally provided, the switching node 2 is connected, and the switching node 18 is disconnected. The supply voltage is provided to the converter 3 serving to supply the direct current voltage to the inverter 7, and to the transformer 13 providing the source voltage to the control circuit 14.
Here, when the control circuit 14, which has received respective output signals from the speed detector 10, the current detector 8 and the load detector 16, applies the voltage command V* to the inverter 7, the inverter 7 provides the alternating current voltages with three phases and three phase frequencies to the induction motor 9, whereby the control circuit 14 serves to control the torque and rotation of the induction motor 9.
In the case in which there occurs a regenerated voltage from the induction motor 9 and the regenerated voltage is detected by the current detector 8, the control circuit 14 turns on the semiconductor device 6, for consuming the regenerated voltage in the resistor 6.
When there occurs an emergency situation such as a power failure, the switching node 18 is connected, whereas the switching node 2 is disconnected. At this time, the emergency power supply 19 converts the direct current voltage outputted from the battery 20 into the three-phase alternating current voltage and the converted voltage is provided to the converter 3 and the transformer 13.
The control circuit 14 being operated by the voltage source provided from the transformer 13 controls the inverter 7 in the same way as when the supply voltage outputted from the power source 1 is provided.
Specifically, as shown in FIG. 5, when the power fails (Step S1), the load detection unit 27 receives the cage load detected (Step S2) by the load detector 16 and judges (Step S3) whether the load weight W.sub.L is more than 50% of the allowed weight. If the judged value is more than 50% of the allowed weight, the driving direction setting unit 21 allows the speed command generator 22 to output the speed command .omega..sub.r * for thereby descending (Step S4) the elevator car; otherwise, the elevator car is ascended (Step S5).
That is, when the speed command .omega..sub.r * is applied to the speed controller 24 which serves to output the current command I*, the current controller 26 which has received the current command I* applies the voltage command V* to the inverter 7 which serves to drive the induction motor 9 for thereby carrying out the car driving operation.
Next, an emergency operation time T.sub.R which has been counted since the start of the car operation, and a set time T.sub.S are compared to each other (Step S6), so that when the emergency operation time T.sub.R is more than the set time T.sub.S, the angular velocity .omega..sub.r is applied (Step 7) to the driving direction setting unit 21 and the first subtractor 23; otherwise, the descending or ascending operation continues until more than the set time T.sub.S is reached.
The driving direction setting unit 21 compares (Step S8) the applied angular velocity .omega..sub.r with the set velocity .omega..sub.st, and when the angular velocity .omega..sub.r is more than the set velocity .omega..sub.st, the elevator car is not set to be driven (Step S9) toward the initial driving direction; otherwise, the driving direction is reversed (Step S10). At this time, the car operation continues until the difference between the angular velocity .omega..sub.y and the angular velocity command in the first subtractor becomes "0" or the difference between the current I and the current command I* becomes "0", for thereby completing (Step 11) the rescuing operation of the elevator system.
However, in the conventional emergency control apparatus, the elevator car driving direction is dependent upon an output signal from the load detector 16 installed between the elevator casing 29 and the cage 15, as shown in FIG. 3, and therefore if the vibration-absorbing rubbers 30 provided adjacent to the load detector 16 are not functional, the emergency driving time becomes disadvantageously longer when the power fails. That is, the vibration-absorbing rubbers 30 are difficult to install and further suffer wears as time lapses, thereby interrupting an accurate detection of the load weight W.sub.L as well as elongating a rescue time due to a possible erroneous operation of the elevator car.